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  • 1
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Description / Table of Contents: ESCA-Spektren von Poly(vinyliden fluorid), Poly(tetrafluoräthy1en) und Copolymeren von Tetrafluoräthylen und Äthylen wurden beobachtet. Dabei wurde festgestellt, daβ CK-Peaks in Dubletts aufgespalten werden, die —CF2— Einheiten in kristallinen Bereichen, den Windungen von —CF2— Einheiten im amorphen Bereich und —CH2—Einheiten im gesamten Polymer zugeordnet wurden. Der Kristallisationsgrad wurde anhand dieser Zuordnung abgeschätzt und mit den Ergebnissen der Röntgenstrahlbeugung verglichen. Die chemischen Verschiebungen der CK-Peaks wurden qualitativ mit der kritischen Oberflächenspannung verglichen. OK-Peaks wurden ebenfalls beobachtet und ihre relativen Intensitäten zum Gehalt an adsorbierten Gasen, wie z. B. O2, H2O und anderen, in Beziehung gesetzt.
    Notes: ESCA spectra of poly(vinylidene fluoride), polytetrafluoroethylene and copolymers of tetrafluoroethylene and ethylene were observed. CK peaks of them were split into doublets, which were assigned to —CF2— units in crystalline regions and the convolution of —CF2— units in amorphous regions and —CH2— units in the polymers as a whole. The degree of crystallinity was estimated according to the above assignment and compared with that from diffraction patterns. The chemical shifts of CK peaks were qualitatively compared with the critical surface tension. OK peaks were also observed in the polymers examined, and the relative intensities of them could be correlated with the content of absorbed gas such as O2, H2O, and others.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    New York : Wiley-Blackwell
    Journal of Polymer Science: Polymer Physics Edition 13 (1975), S. 929-946 
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Persistent polarization in poly(vinylidene fluoride) (PVDF) thermoelectrets prepared under high electric field strengths has been studied by measurements of surface charge and piezoelectricity. An anomalous heterocharge appears after the normal homocharge disappears. A model is proposed to explain the surface charge phenomena; the anomalous heterocharge is expressed as a sum of a hidden homocharge and a hidden heterocharge. It is concluded that the anomalous heterocharge as well as the apparent homocharge are not responsible for the piezoelectricity of PVDF electrets. The piezoelectricity is shown to depend on the structure of the original PVDF films or the amount of β-form crystals. However, the piezoelectricity is not attributed to stress dependence of the spontaneous polarization in the β-form crystal of PVDF, but to the hidden polarization which bring about the anomalous heterocharge. The hidden polarizations are attributed to trapped charges.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: Persistent polarization in poly(vinylidene fluoride) thermoelectrets prepared under high electric field has been studied by measurements of depolarization and pyroelectricity. Various polarizations are examined in detail; the polarizations related to a characteristic molecular motion near 60°C and the polarizing temperature are not responsible for the major piezoelectric effect in β-form electrets. The piezoelectricity is attributed to a polarization appearing near the melting temperature. The persistent polarization corresponding to d31 of 2 × 10-11 coul/N is about 5 × 10-6 coul/cm2. The pyroelectricity of β-form electrets is linearly correlated with the piezoelectricity.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 0098-1273
    Keywords: Physics ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The piezoelectricity of PVDF thermoelect rets formed with vacuum-coated aluminum electrodes has been investigated in detail. The piezoelectricity depends on the β-form crystal structure of PVDF homopolymer and copolymers. However, the piezoelectricity is not attributed to the stress dependence of the spontaneous polarization of β-form crystals, but rather to the persistent polarization arising from trapped charges. The trapping mechanism is discussed.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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